Nitrogen flow and environmental risk in relation to agriculture in Japan

Residual nitrogen on agricultural fields, due to the difference between inp uts (fertilizer, manure, etc.) and outputs (cropping, denitrification), is thought to be one of the environmental risks caused by agricultural practic e. Nitrogen in nonutilized livestock wastes discharged to the environment a lso cause environmental risk. These factors will cause environmental proble ms such as the degradation of water quality and, therefore degrade the sust ainability of agriculture. In this study, we estimated these nitrogen flows due to agricultural practice in each of 47 prefecture in japan by using a database for estimating nitrogen flow in a region. Residual nitrogen on farmland in Japan was estimated at 92 kg ha(-1) and it ranged from 46 to 225 kg ha(-1) among prefectures. Non-utilized livestock waste in Japan was 17 kg ha(-1) and it ranged from 2 to 69 kg ha(-1) among prefectures. Though residual nitrogen on farmland may be affected by high application of chemical fertilizer, dispersion of residual nitrogen and nonutilized lives tock waste indicate the mitigation plans are different in each prefecture. For this purpose, we pick up 2 characteristic prefectures and simulated the changes of residual nitrogen and non-utilized livestock waste when farming methods that have been developed to reduce environmental risks were incorp orated.